1. Field of the Invention
The present invention relates to a method for controlling the focus speed of a pick-up head, and more particularly, to the method for controlling the focus speed of the pick-up head while performing a layer jump operation over a multi-layer optical disk in an optical information reproducing device.
2. Description of the Related Art
An optical information reproducing device, such as CD-ROM DVD-ROM CD-RW DVD-RAM, has been widely applied in multimedia computer systems and becomes one basic element of the computer systems. Some U.S. Pat. Nos., i.e. 4,783,774, 5,289,097, 5,246,479 and 5,345,347 may be referred in order to have an in-depth understanding of the optical information reproducing device.
Please refer to FIG. 1. FIG. 1 shows a function block diagram of a conventional optical information reproducing device 10. Typically, an optical information reproducing device 10 includes a pick-up head 12, a pre-amplifier 14, a digital signal processor 16, a microprocessor 18, a servo controller 20, a driver circuit 22 and an actuator 24. The pick-up head 12 is for reading data stored on an optical disk 26. The pre-amplifier 14 is electronically connected to the pick-up head 12 for amplifying the signal of data read from the optical disk 26 and generating an analog signal of reading data. The digital signal processor 16 is electronically connected to the pre-amplifier 14 for receiving the analog signal of reading data and generating a digital signal of reading data. The microprocessor 18 is electronically connected to the digital signal processor 16 for processing the digital signal of reading data according to a predetermined procedure. The servo controller 20 is electronically connected to the microprocessor 18, digital signal processor 16 and pre-amplifier 14 for detecting and processing the signal of servo data read from the optical disc 26, wherein the servo data includes servo burst, synchronous pulse and track number etc. The driver circuit 22 is electronically connected to the servo controller 15 for providing an actuating driving signal. The actuator 24 is electronically connected to the driver circuit 22 and pick-up head 12 for driving the pick-up head 12 to different radial positions in response to the actuating driving signal, or kicking an objective lens (not shown) of the pick-up head 12 to a focus on the optical disk 26 in response to another actuating driving signal.
Please refer to FIG. 2. FIG. 2 shows a schematic diagram of traditionally focusing a dual-layer optical disk 26. While the optical information reproducing device 10 is applied to a dual-layer optical disk 26 for performing a layer jump operation, the objective lens of the pick-up head 12 will move from a first focus 27 to a second focus 28 over the optical disk 26. First of all, the digital signal processor 16 sends a kick pulse signal 29 in response to a layer jump command of the microprocessor 18. The kick pulse signal 29 is then sent to the actuator 24 through the servo controller 20 and driver circuit 22. The actuator 24, in response to the kick pulse signal 29, kicks the objective lens of pick-up head 12 out of the first focus 27 of the optical disc 26. When the objective lens moves closely to the second focus 28 of the optical disk 26, the digital signal processor 16 sends a brake pulse signal 25 in response to a brake command of the microprocessor 18. The brake pulse command 25 is then sent to the actuator 24 through the servo controller 20 and driver circuit 22. The actuator 24 locks the objective lens of the pick-up head 12 over the second focus 28 of the optical disk 26.
Please refer to FIG. 3 and FIG. 4. FIG. 3 shows a relative control signal diagram of the objective lens while unlocking the second focus 28. FIG. 4 shows another relative control signal diagram of the objective lens while unlocking the second focus 28. Focus error signal Se shown in FIG. 3 and FIG. 4 represents an error signal of the relative position between the objective lens and focus 27 and 28, which is generated by the pick-up head 12. Control pulse signal Sc shown in FIG. 3 and FIG. 4 represents a force signal for driving the objective lens, which is generated by the digital signal processor 16. RF Level signal Sr shown in FIG. 3 and FIG. 4 represents a reading intensity signal of the pick-up head 12, which is generated by the pick-up head 12. However, due to the deviation of the optical disk 26 and the difference of the actuator 24, while the optical information reproducing device 10 performing the layer jump operation on dual-layer disk 26, it is not able to predict precisely the speed with which the objective lens moving closely to the second focus 28 of the optical disk 26. If the relative speed between the objective lens and the second focus 28 is too high and the braking force applied to the objective lens is constant, the objective lens often overshoots and unlocks the second focus 28, wherein the focus error signal Se has a diversifying trend with time as shown in FIG. 3. On the other hand, if the objective lens can""t reach the second focus 28 in time, it also won""t be able to react immediately and speed up the objective lens to lock the second focus 28 as shown in FIG. 4. Therefore while performing the layer jump operation over the dual-layer disk 26, the conventional control method of the focus speed is unstable with respect to the objective lens of the optical information reproducing device 10.
It is therefore an objective of the present invention to provide a method for controlling a focus speed of a pick-up head to solve the above mentioned problem.
In a preferred embodiment, the present invention provides a method for controlling a focus speed of a pick-up head while performing a layer jump operation over a multi-layer optical disk in an optical information reproducing device. The optical information reproducing device includes the pick-up head, an actuator and a counter. The pick-up head has an objective lens positioned over a first focus of the multi-layer optical disk, in response to a signal reflected from the multi-layer optical disk, will generate a RF level signal. The actuator is electronically coupled to the pick-up head for driving the objective lens to perform the layer jump operation in response to a kick pulse signal. The counter generates a counter value in response to the kick pulse signal. The method comprises the steps of sending the kick pulse signal to the actuator for kicking the objective lens out of the first focus; processing the RF level signal and the counter value for generating a speed control data according to a predetermined procedure; and driving the objective lens to a second focus through the actuator in response to the speed control data. When the closing speed between the objective lens and the second focus is too high, the actuator will apply a greater braking force on the objective lens. When the closing speed between the objective lens and the second focus is too low, the actuator will apply a weaker braking force on the objective lens. If the objective lens can""t reach the second focus in time, the actuator will apply a speeding force on the objective lens. Therefore, the optical information reproducing device applied with the method of the present invention will have a stable layer jump operation.
This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various drawings and figures.